Current structural designs for bridges, buildings and supporting spans for elevated rail systems often require elongated, pre-stressed structural beams. Increasingly, massive structures exceeding 160 feet in length and 160,000 lbs. must be moved from manufacturing sites to construction areas over state and federal highways. Because of road safety and weight limitations state and federal authorities have adopted highway weight distribution formulae and regulations which determine legal load limits for load carrying vehicles, the manner in which the load carrying vehicles may traverse a highway, and the weight distribution of load-carrying vehicles over the pavement. Typically these weight distribution formulae are used to prescribe load limits for individual axles or axle clusters and the distribution of the load weight over the pavement.
Very heavy loads exceeding the regulated weight limits often require special permits from state authorities. Although criteria for these permits may vary from state to state the load-carrying vehicles must normally comply with a distribution formula determined by the government authorities for safe travel across highways.
Another common problem is the hauling of massive loads over bridges. Loads normally cannot traverse a bridge span when they exceed 60,000 lbs. per span. A third problem associated with load-carrying vehicles known in the prior art occurs when the load, e.g. a beam, is moved on to the construction site. Beams and trusses must be accurately positioned so that cranes can lift them without the danger of tipping. In the past it has at times been an arduous and time consuming task to accurately position a long load in order for cranes or other equipment to grasp the load and situate it in its final position. Another problem is the limited speed of vehicles transporting these heavy loads. Since delays in major construction projects often result in substantial cost impacts it is particularly important that beams move under the safest, fastest possible means from the manufacturing site to the construction site.
With recent increases in the length and mass of precast structures, attempts in the prior art to solve these or similar problems for smaller loads are not applicable to structures exceeding 160,000 lbs. Examples of prior art applicable to transporting smaller loads include U.S. Pat. Nos. 2,741,489; 3,438,652; and 4,441,730. U.S. Pat. No. 3,438,652 discloses a snobble trailer which provides a steerable aft dolly having only three steering positions. U.S. Pat. No. 4,441,730 requires a connectable, trailerable device for steering the aft end. U.S. Pat. No. 2,741,489 also requires a connection from the aft to the fore-trailer to provide steering. Notwithstanding these and other advances in the prior art, it is desirable to have a safer and more efficient load-carrying vehicle for transporting structural members exceeding 160 feet in length and 150,000 lbs. This invention has been developed for the purpose of obviating the aforesaid limitations of the prior art.